This invention generally relates to the use of microwave energy to accelerate the rate at which a chemical preserving solution penetrates the walls of cells to provide tissue fixation, and more particularly relates to apparatus and method for batch fixating a plurality of tissue specimens.
As is well known, pathologists diagnose diseases by examining tissue specimens or samples from a biopsy or other similar medical procedure. Because it is important that the cells be examined in a state as close to the living state as possible, the tissue specimens are typically put through a chemical fixation process in order to stop the cells from degrading. More specifically, the specimens are typically emersed in a preserving solution which commonly includes formaldehyde. The preserving solution penetrates the walls of the cells and hardens the cell structure thereby preventing or greatly retarding subsequent cell degradation. A pathologist then subjects the specimens to various tests and examinations for diagnosis.
One significant problem of the above described fixation process is that it takes a relatively long period of time such as, for example, 4-8 hours for the preserving solution to penetrate cell walls. Accordingly, the fixation process may prevent a relatively fast diagnosis. Also, at least during the early stages of fixation, the cells may continue to degrade. The delay may cause the cells to change from their original living state and thus, in some cases, the proper diagnosis may be prevented or clouded.
Microwave energy has been used to speed up the rate at which the preserving solution penetrates cell walls during fixation. In the typical procedure, a tissue specimen or sample is placed in a vial containing a formaldehyde solution, and then the vial is exposed to microwave energy in a microwave oven. For reasons not fully understood but believed to be related to the vibration of molecules, the presence of the microwave field greatly increases the rate at which the fixation solution penetrates the cell walls. For example, the presence of a microwave field may reduce the typical fixation time period from several hours down to about one minute. This is important not only because it saves processing time, but also because the cells have less time to degrade and therefore the quality of the fixated tissue may be enhanced.
One microwave tissue fixating apparatus is described in U.S. Pat. No. 4,891,239 which is assigned to the same assignee as the present invention, and which is hereby incorporated by reference. Such apparatus has a single mode waveguide with a small aperture through which a vial containing a tissue specimen and the fixating solution is inserted. With such arrangement, the submerged specimen is exposed to a relatively uniform field of microwave energy, and the amount of microwave energy absorption in the specimen can be accurately controlled. Thus, favorable fixating results have been attained using this apparatus. However, one drawback of such apparatus is that it is not generally suitable for high volume production because only a single or just a few specimens can be simultaneously fixated. More specifically, there are limitations in the number and size of apertures that can be provided in a single mode waveguide and provide suitable impedance matching for vials inserted therein. Further, if a plurality of specimens were placed longitudinally along a waveguide, they would generally be exposed to different amounts of microwave energy thus resulting in non-uniform fixating results from specimen to specimen.
Conventional microwave ovens have been used to assist in tissue fixation. However, the distribution of microwave energy in a conventional microwave oven is not generally uniform enough so that a large plurality of tissue specimens can be simultaneously processed in batch operation with substantially identical and controlled results from specimen to specimen. Although rotating feed antennas and rotating turntables have generally improved the field uniformity in microwave ovens, the cavities of such microwave ovens still have so-called hot and cold spots. That is, the spacial distribution of energy is not uniform, and therefore the rate at which a lossy item absorbs microwave energy is a function of its spacial location within the microwave oven cavity. Also, there may be non-uniform exposure and hence absorption of microwave energy within a given specimen. Such non-uniform energy distribution is not suitable for batch processing tissue specimens because each specimen generally requires a relatively precise and controlled amount of exposure to microwave energy so as to fixate properly. If a vial in one spacial location receives the proper amount of exposure, another vial in another spacial location may receive too much or too little microwave exposure. If a specimen receives too much exposure, it will start to cook and important artifacts in the cells may be obscured or destroyed. On the other hand, if a specimen receives too little exposure, fixation may be incomplete and therefore not enough preserving solution will penetrate the cell walls to stop cell degradation.